Welcome to HVAC-Talk.com, a non-DIY site and the ultimate Source for HVAC Information & Knowledge Sharing for the industry professional! Here you can join over 150,000 HVAC Professionals & enthusiasts from around the world discussing all things related to HVAC/R. You are currently viewing as a NON-REGISTERED guest which gives you limited access to view discussions

To gain full access to our forums you must register; for a free account. As a registered Guest you will be able to:

Participate in over 40 different forums and search/browse from nearly 3 million posts.

Temp rise on heat pumps

Good afternoon Gentlemen,

I am a junior tech who is struggling to understand temp rise on heat pumps. First and most importantly I would kindly like to know the general procedure to inspect temp rise on heat pumps, if there is any. I have asked around in my company for the general procedure, but it seems like I am beating around the bush.

When I go to homes, I bump up the tstat one degree to confirm 1st stage, this is when I will also get the temp rise (which I have been told that it should be 20 degrees, just like temp drop but only the opposite, fair enough). The only problem is that, everytime I do this the heating elements come on, and I able to tell this because my temp rise is no longer 20 degrees rather it spikes to 40 degrees.

I know tstats could be configured so that if I bump up the tstat 3 degrees the elements kick in, but that rarely happens...everytime Iam bumping up the tstat 1 degree, the heating elements are coming on...and ofcourse, most folks do not know how to operate the heat pump, they are just happy they are getting heat....my real question is, " what should be a temp rise on heat pumps, and why are these thermostats I am running into have auxiliary heat turned on everytime I turn on the tstats ? "

Anyhow, if someone can explain me a bit about this confusion, it would be a great help. Thanks for your time.

I am a junior tech who is struggling to understand temp rise on heat pumps. First and most importantly I would kindly like to know the general procedure to inspect temp rise on heat pumps, if there is any.

As said above disable the aux heater by removing the wire that active them at the t-stat or hair handler ( I always found doing it at the t-stat was easier, side note: leave your car keys at the stat so you can"t leave with reconnecting the wire).

Run the heatpump for at least 10 minutes, then measure your split:

CFM x ∆T X .317 = Watts output

Watts output x 3.412 = BTUH

A stating point for the output should be 47°. Thats where you should be near the nominal sizing of the heatpump...... IE: A 3 ton HP will make about 36K BTUH worth of heat (this is in place of having actual application data for the system you are checking).

If you want to determine the CFM moving over the system, before disconnecting the aux heat at the t-stat run the aux heat by itself at the same fan speed as the heatpump will operate at and record the ∆T after 5 mins of operation and use the following formula:

Amps x volts / ∆T x 3.16 = CFM

Do this 10 times and you'll have the entire routine down to about 30 minutes to really calculate a value that means something.

The reason you get no help from anyone on what a ball park ∆T is for a HP is because there is none on an air source unit. The goal posts keep moving as the outdoor temps move. Calculating the output and estimating the target is the only was to do it .

Rundawg is correct, delta T in heat mode also includes the heat of compression and the heat added by the compressor motor. In cool mode this is rejected at the condenser ( ever heard the ambient + 30* rule of thumb for condenser air off temperature?) Remember though correctly sized ductwork and proper airflow play a big part in this number.

I thought the temp rise was low and the pressures for low side to be high too, now that I am starting to make some sense of heat pumps I will start to inspect them thoroughly, as I am noticing the installers or the initial builders/contractors are not properly wiring/installing these machines. And I feel so bad for the customers as they have no clue whats going on with there electric bills, they are happy campers as long as they are getting heat.

The compressor was amping at 6.9amps (I think this is sufficient for a goodman), and yeah the temp rise was also taken at the a/h. The customer told me she previously had air flow problem in her bedroom so the company added an additional return right beneath the a/h, since then she says the air flow has improved.

she had a white rogers tstat, where the white(heat) was connected to W1 and jumped to E terminal. I guess normal setting for a heat pump ?

I checked her filter, it was clean. This was R22 system.

Beenthere, you are right. Her two 5kw elements were connected to one sequencer (which were amping at 19.2amps) and the one that was not responsive was connected to separate sequencer, hence it wasn't sensing enough cold air to energize the third element.

BY the way she did have a variable motor also, maybe this has something to do with the odd low side pressure ?